From: Linus Torvalds <torvalds@linux-foundation.org>
To: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc: Sparse Mailing-list <linux-sparse@vger.kernel.org>
Subject: Re: [PATCH 1/7] not: add testcases for canonicalization & simplification of negations
Date: Sun, 22 Nov 2020 11:00:26 -0800 [thread overview]
Message-ID: <CAHk-=wjqwFDEJkGoPtjeTn1cDDpadz_eL_m1w-wk9G9Zmucosg@mail.gmail.com> (raw)
In-Reply-To: <20201122152731.10994-2-luc.vanoostenryck@gmail.com>
I thought we already canonicalized the pseudo ordering, but clearly not..
Anyway., looks good to me.
Btw, if you want to do another simplification, one that I've actually
seen multiple times in the kernel is this one:
if (val1 & BITx)
val2 |= BITy;
and turning it into
val2 |= (val1 & BITx) .. shift left or right by (BITx-BITy);
and while actually testing the above, I note that sparse seems to have
problems with even simple if-conversion:
#define BIT1 4
#define BIT2 8
int fn(int x, int y)
{
if (x & BIT1)
y |= BIT2;
return y;
}
linearizes to a nasty mess of actual phi nodes and conditional jumps
rather than just a 'select' op. Never mind the actual unconditional
version, of course.
I didn't check why the if-conversion doesn't happen.
Linus
next prev parent reply other threads:[~2020-11-22 19:01 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-22 15:27 [PATCH 0/7] simplify logical negation Luc Van Oostenryck
2020-11-22 15:27 ` [PATCH 1/7] not: add testcases for canonicalization & simplification of negations Luc Van Oostenryck
2020-11-22 19:00 ` Linus Torvalds [this message]
2020-11-22 19:57 ` Luc Van Oostenryck
2020-11-22 20:13 ` Linus Torvalds
2020-11-22 20:38 ` Luc Van Oostenryck
2020-11-22 22:26 ` Luc Van Oostenryck
2020-11-27 22:25 ` [PATCH 0/6] 'bits translation' simplification Luc Van Oostenryck
2020-11-27 22:25 ` [PATCH 1/6] add testscases for 'bits translation' optimization Luc Van Oostenryck
2020-11-27 22:25 ` [PATCH 2/6] factorize SEL(x, OP(y,z), y) into OP(SEL(x, z, 0), y) Luc Van Oostenryck
2020-11-27 22:25 ` [PATCH 3/6] add helper is_power_of_2() Luc Van Oostenryck
2020-11-27 22:25 ` [PATCH 4/6] add helper is_pow2() Luc Van Oostenryck
2020-11-27 22:25 ` [PATCH 5/6] add log base 2 function: log2_exact() Luc Van Oostenryck
2020-11-27 22:25 ` [PATCH 6/6] convert SEL(x & BIT1, BIT2, 0) into SHIFT(x & BIT1, S) Luc Van Oostenryck
2020-11-27 22:25 ` [PATCH 7/7] move up instructions blocking if-conversion Luc Van Oostenryck
2020-11-27 22:44 ` [PATCH 0/6] 'bits translation' simplification Linus Torvalds
2020-11-22 15:27 ` [PATCH 2/7] canon: put PSEUDO_ARGs in canonical order too Luc Van Oostenryck
2020-11-22 15:27 ` [PATCH 3/7] canon: put PSEUDO_REGs " Luc Van Oostenryck
2020-11-22 15:27 ` [PATCH 4/7] canon: simplify calculation of canonical order Luc Van Oostenryck
2020-11-22 15:27 ` [PATCH 5/7] opcode: add helpers opcode_negate() & opcode_swap() Luc Van Oostenryck
2020-11-22 15:27 ` [PATCH 6/7] not: simplify (~x {&,|,^} x) --> {0,~0,~0} Luc Van Oostenryck
2020-11-22 15:27 ` [PATCH 7/7] not: simplify ((x cmp y) {&,|,^} (x !cmp y)) --> {0,1,1} Luc Van Oostenryck
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